Vent system for cpap patient interface used in treatment of sleep disordered breathing

ABSTRACT

A vent assembly for use with a mask assembly includes a first vent and a second vent having at least one different flow characteristic wherein the vent assembly can be switched between the first vent and the second vent to alter flow of exhaled gas from a patient.

CROSS REFERENCE TO PRIORITY APPLICATIONS

This application claims priority to U.S. Provisional Applications Nos.60/524,728, filed Nov. 25, 2003, 60/538,507, filed Jan. 26, 2004 and60/550,319, filed Mar. 8, 2004, each incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The invention relates to a vent system for use with a ContinuousPositive Airway Pressure (CPAP) patient interface, e.g. a mask, used intreatment of Sleep Disordered Breathing.

BACKGROUND

The use of nasal CPAP apparatus to treat “snoring sickness” waspioneered by Sullivan and taught in U.S. Pat. No. 4,944,310. Nasal CPAPapparatus typically comprises a blower, an air delivery conduit and apatient interface. The blower provides a supply of air or breathable gasat positive pressure. The conduit interconnects the blower and thepatient interface. A variety of nasal masks, nose & mouth masks, fullface masks, nasal prongs and nasal pillows are used to provide aninterface with the patient.

A typical mask comprises:

-   (i) a rigid or semi-rigid portion, termed a shell or frame, which    defines a nose-receiving cavity; and-   (ii) a soft patient contacting portion, termed a cushion or    membrane.    Cushions have been constructed from silicone, foam, gel and    combinations of these materials.

Since a patient typically exhales into the same mask cavity wherefromthey inhale, the possibility of rebreathing of carbon dioxide (CO₂)exists. In conjunction with a sufficient continuous flow of fresh air orbreathable gas, a vent can allow a controlled leak from the mask cavityand hence provide for the washout of CO₂. Unfortunately, the noise ofair or breathable gas from the vent can disrupt anyone within earshotattempting to sleep. Hence there is an advantage in providing alow-noise vent.

One form of known vent is described in U.S. Pat. Nos. 6,561,190 (Kwok)and 6,561,191 (Kwok). These patents describe the use of grommet in amask frame. The contents of these patents are hereby incorporated bycross-reference. A vent in accordance with embodiments of theseinventions is found in the MIRAGE™ mask, manufactured by ResMed Limited.

Another known form of vent is described in International PatentApplication PCT/AU00/00636 (Drew et al.) published as WO 00/78381. Thispatent application describes the use of a connector for a mask having avent along a smooth continuing surface. The contents of this patentapplication are hereby incorporated by cross-reference. A vent inaccordance with an embodiment of this invention is found in the ULTRAMIRAGE™mask, manufactured by ResMed Limited.

Another known form of vent is described in U.S. Pat. No. 6,581,594 (Drewet al.). This patent describes the use of a vent which, in one form,comprises a thin air permeable membrane. The contents of this patentapplication are hereby incorporated by cross-reference.

Another known form of vent is described in International PatentApplication PCT/AU01/01658 (Dantanarayana et al.) published as WO02/051486. This patent application describes the use of a flowregulation vent. The contents of this patent application are herebyincorporated by cross-reference.

U.S. Pat. No. 6,557,555 (Hollis) describes a vent valve apparatus. Thecontents of this patent application are hereby incorporated bycross-reference.

Another known vent is the Respironics WHISPER swivel.

European Patent No. 0 697 225 discloses a vent formed from a poroussintered material.

A known vent, manufactured by Gottleib Weinmann Geräte Für Medizin UndArbeitsschutz GmbH and Co. comprises a generally cylindrical insert tobe interposed in use, between the mask shell and the gas conduit. Theinsert includes a window which is covered with a porous sinteredmaterial of approximately 3-4 mm thickness.

Another type of vent intended to be inserted between the mask shell andthe breathable gas supply conduit is the E-Vent N by Draegermedizintechnik GmbH (the Draeger vent). The Draeger vent comprises astack of 21 annular disks, which have slots in their adjacent surfacesfor gas to flow therethrough. Each slot has a length of 5 to 7 mm asmeasured along the path from the interior of the vent to atmosphere.

Typically vents are designed with sufficient porosity to provide enoughvent flow at a low pressure (e.g. 4 cmH₂O) to ensure adequate washout ofCO₂.

Reducing the pore size of a vent can make the vent quieter, but can alsoincrease the chances that the vent will clog.

Problems with prior art vents include that they can be too noisy, thatthey clog with dirt and moisture (particularly when used withhumidifiers), that they are awkward or difficult to clean or assembleand that they have designs which are sensitive to very small changes inthe manufacturing process which can lead to variation in the pressureflow relationship.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention there is provided avent for a CPAP patient interface.

In accordance with a second aspect of the invention there is provided avent assembly comprising at least two alternative vents each havingsubstantially the same pressure-flow characteristics.

In accordance with a third aspect of the invention there is provided avent assembly comprising at least two alternative vents each havingdifferent pressure-flow characteristics.

In accordance with another aspect of the invention there is provided avent assembly comprising at least two alternative vents and a mountadapted to support at least one vent in a venting position.

In accordance with another aspect of the invention there is provided avent assembly comprising at least two alternative vents and a mountadapted to support at least one vent in a venting position and a lockingmechanism adapted to retain said at least one vent in a ventingposition.

In accordance with still another aspect, there is provided a maskassembly for a patient comprising a frame, a cushion provided to theframe, and a vent assembly including a first vent, a second vent, and aselector to switch the flow of exhaled gas from the patient between thefirst and second vents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a prior art blower, air deliveryconduit and patient interface.

FIG. 2 shows a related art mask with swivel elbow.

FIG. 3 shows a cross-section of a related art patient interface inposition on a patient's face with swivel elbow.

FIG. 4 a-c show side views, a cross section and a detail of a swivel inaccordance with a first embodiment of the invention.

FIG. 5 a-c shows a swivel in accordance with a first embodiment of theinvention in three positions.

FIG. 6 shows an exploded perspective view of a swivel elbow inaccordance with a second embodiment of the invention.

FIG. 7 shows a swivel elbow assembly in accordance with a secondembodiment of the invention with the vent in a “coarse” hole position.

FIG. 8 shows a swivel elbow assembly in accordance with a secondembodiment of the invention with the vent in a “fine” hole position.

FIG. 9 shows a swivel elbow sleeve in accordance with a secondembodiment of the invention.

FIG. 10 shows a swivel elbow assembly in accordance with anotherembodiment of the invention, suitable for use with a RESMED ULTRA MIRAGEmask.

FIGS. 11 a and 11 b show a sliding vent assembly in accordance with anembodiment of the invention.

FIG. 12 shows a further view of the vent assembly of FIG. 11 a.

FIG. 13 shows a drawing of the vent assembly of FIG. 11 a.

FIG. 14 shows an alternative view of the vent assembly of FIG. 11 a.

FIG. 15 shows a front view of a swivel elbow with vent assembly inaccordance with a first embodiment of the invention.

FIG. 16 shows a side view of a swivel elbow with vent assembly inaccordance with a first embodiment of the invention.

FIG. 17 shows a front view of an assembly including mask frame andswivel elbow with vent assembly in accordance with a first embodiment ofthe invention.

FIG. 18 shows a side view of the assembly of FIG. 17.

FIG. 19 shows a perspective view of the assembly of FIG. 17.

FIG. 20 shows an embodiment of the invention which incorporates visual,tactile and aural feedback of vent position.

FIG. 21 shows an embodiment of the invention which incorporates anelectrical resistance sensor.

FIG. 22 shows an embodiment of the invention with a slidable vent coverexposing a set of larger holes.

FIG. 23 shows an embodiment of the invention with a slidable vent coverexposing a set of smaller holes.

FIGS. 23 a-23 c illustrate still another embodiment of the presentinvention.

FIG. 24 shows an embodiment of the invention with a hinged vent cover.

FIGS. 25 a and 25 b show an alternative embodiment of the inventionincorporating a rotating vent cover.

FIGS. 25 c-25 e illustrates another alternative embodiment of thepresent invention.

FIGS. 25 f-25 g illustrate yet another embodiment of the presentinvention.

FIG. 26 shows a cartridge-style embodiment of the invention in explodedview.

FIGS. 27 a and 27 b show the cartridge-style embodiment of the inventionin two different positions.

FIGS. 28 a and 28 b illustrate yet another embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a blower 10 connected to an air delivery conduit 20 and theair delivery conduit 20 connected to a patient interface 30. In the viewshown in FIG. 1, the patient interface 30 is a nasal mask. The patientinterface 30 includes a vent 40. The vent 40 includes one or more holes,e.g., six holes 50.

FIG. 2 shows an alternative nasal mask, the MIRAGE® ACTIVA™ nasal mask.This mask includes a swivel elbow 60. The swivel elbow is described infurther detail in the Applicant's co-pending International PatentApplication PCT/AU03/01162, the contents of which are herebyincorporated by cross-reference. The swivel elbow 60 includes a ventcover 70 having a number of holes 50 therethrough.

FIG. 3 shows a cross-section of a patient interface 30 in position on aface of a patient 80. A swivel elbow 60 is shown detached and in frontof the patient interface 30.The cavity 90 into which the patient 80 canexhale nasally can accumulate carbon dioxide unless it is washed outthrough the vent 40 included in the elbow 60.

In a first embodiment of the invention, a vent assembly is provided withtwo alternative vents, vent a and vent b as shown in FIG. 4 a-5 c. Bothvent a and vent b provide approximately the same total flow. Vent aprovides relatively fewer large vent holes, whereas vent b provides amatrix of relatively smaller holes (e.g. below 0.5 mm diameter,preferably approximately 0.1 mm in diameter). Selection between vent aand vent b is made by rotating or sliding a cover so that either thesmall or large holes are lined up with an orifice on a mating surface.

As shown in FIGS. 4 a and 4 b in exploded views, a vent assembly 90 inaccordance with an embodiment of the invention comprises a generallycylindrical first portion 100 and a generally cylindrical sleeve portion110. The first portion 100 includes an orifice or window 102. The sleeveportion 110 includes, in one embodiment, two alternative sets of holescorresponding to vents a and b respectively. Vent a uses three largeholes. Vent b uses a series of smaller holes. In use the sleeve portion110 rotatingly fits over an end of the first portion 100. In theembodiment of the invention shown in FIG. 4 a, the sleeve is free torotate through 180° degrees as shown by the arrows in FIG. 5 a-5 c,although in other embodiments the sleeve may rotate through fewerdegrees. As shown in FIG. 4 a-4 b, both the first portion 100 and sleeveportion 110 are hollow which allows air to pass between the interior ofthe first portion 100 through window 102 and thence through either ofvent holes a orb. FIG. 4 c shows a detail of the vent with small holes.

In a second embodiment of the invention the vent assembly is formed aspart of a swivel elbow 120, for example, the swivel elbow used on theMIRAGE® VISTA™ mask, manufactured by ResMed Limited, as shown in FIG.6-9. The elbow 120 includes a shaft 130 with an orifice 132 therein. Theshaft 130 includes an alignment tab 134. A sleeve 140 includes a pair ofalternative vents 142, 144 and a pair of slots 146, 148, each oneassociated with one vent, each adapted to receive the alignment tab ofthe shaft. In use, the orifice 132 of the shaft 130 aligns with eithervent 142 or vent 144. In order to change from one vent to another, thevent assembly is pulled apart, rotated 180°, and re-assembled. In thisway, at least one of and only one of vents 142 or 144 is used at onetime.

In a third embodiment of the invention the vent assembly includes amoving part. The moving part can be located in each of two positions byhaving a protrusion on one part match a depression on the matching part.Alternatively, the two positions can simply be defined by use ofappropriate positioning structure, e.g., detents, ratchets, etc. Whenthe vent assembly is partway between the two vent positions, theprotrusion can act to separate the matching parts so that the ventedairflow is greater than in either of the two correct positions. Thisprovides a fail-safe mechanism where an incorrect position results inhigh airflow (a safe condition) and also higher noise (warning the userof the mistake). Generally speaking, the assembly can be configured suchthat a warning, e.g., a noise, can be created when the vent parts aremisaligned.

A typical vent comprises a number of vent holes. For example, three ventholes with a diameter of 2.7 mm. The effective area of a vent hole isgenerally smaller than the actual cross-sectional area of the vent hole.Small holes have a relatively smaller effective area than large holes,e.g. about 10% smaller. The effective area of a vent is the sum ofeffective areas of its constituent vent holes. In one form thealternative vents have the same effective areas.

In another embodiment of the invention, alternative vent constructionsare used instead of using holes. For example, vent a and vent b arelaminar flow elements, such as used in the ULTRA MIRAGE® mask. Inanother form sintered materials are used to construct the vent. Inanother form, vents are constructed from foam polymers. Combinations ofdifferent vents may be used, for example, a vent with holes and a ventconstructed from a sintered material. The assembly may comprise morethan two vents, for example a vent with holes, a sintered vent and alaminar flow element-type vent.

In some cases, such as clinical studies, it is desirable to test theeffectiveness of a particular treatment regime, or mask and compare itwith a suitable control. For example, it might be desired to test theeffectiveness of an algorithm for providing nasal CPAP therapy. In sucha situation, it would be desirable to be able to discount the effect ofwearing the mask per se. This could be achieved by using a “sham” mask,for example, a mask with a very large vent hole. An example of a shammask is taught in published PCT patent application WO 02/066,105. Adifficulty of using a dedicated “sham” mask is that the patient may beaware that they are using the sham mask, or that it may be necessary todisturb their sleep in order to don such a sham mask.

The vent assembly may include a sham vent as an alternative. Such a shamvent would have a very high permeability, e.g. a large hole. By use ofthe invention, it would be possible for a clinician to switch from a“treatment” vent to a “sham” vent, with minimal disturbance to asleeping patient and thus obtain clearer results for a clinical study.

Whilst in a preferred form the different vents are alternatives, in oneform more than one vent may be used at once, for example, ½ vent a and ½vent b.

In a vent comprising vent holes, increasing or decreasing the number ofholes in the vent allows the vent flow to be set to any desired level.In this way a vent assembly in accordance with the invention can bedesigned to have pressure flow characteristics that mimic prior artmasks which use vents with holes.

A variety of materials may be used to construct the vent assembly, forexample, polycarbonate (e.g. MAKROLON), or other polymers, stainlesssteel, sintered ceramic or PTFE, and foam polymers. It may beparticularly advantageous to use hydrophobic materials such as PTFE forsmall pored vents to reduce clogging of pores.

In an alternative form, instead of being mounted on a swivel elbow, avent assembly 200 in accordance with an embodiment of the invention ismounted on or formed as part of a patient interface frame 210. FIGS. 11a-14 show a frame for a patient interface which comprises two generallycylindrical end portions 220 interconnected by a generally rectangularbackbone 230. A clip 240 is slidably positioned on the backbone 230. Theclip 240 includes at least two alternative vents 250, 260. One or moreorifices or windows in the backbone 230, similar to orifice or window102, provides for fluid communication to an interior of the patientinterface. By sliding the clip 240 to alternatively align vent 250 or260 with the orifice, exhaled air can be vented via vent 250 or 260.FIG. 11 a shows the clip 240 in a first position in which the vent 260is aligned with an orifice in the backbone, and one or both vents 250are sealed. FIG. 11 b shows the clip 240 in a second position in whichone or both vents 250 are aligned with respective orifices in thebackbone, and the vent 260 is sealed.

FIGS. 22 and 23 show an alternative embodiment of the invention in anasal mask 300. This form of the invention includes a slidable ventcover 310 which in a first position 305 exposes a set of large ventholes 320 and in a second position 315 exposes a set of small vent holes330. In one form the large and small vent holes are molded into asilicone grommet 325 which is removably insertable into a mask frame, ina similar manner to U.S. Pat. Nos. 6,561,190 and 6,561,191 (Kwok). Whenholes are exposed the passage of air between the interior of the maskand the exterior of the mask can occur therethrough.

FIG. 23 a illustrates another embodiment of the present invention havinga mask assembly 700 with a shell 702 and a cushion attached or otherwiseprovided to the shell 702. The shell 702 includes an aperture 706 bywhich pressurized breathable gas is provided to an interior chamberdefined by the shell 702 and cushion. Alternatively, a swivel elbow maybe provided to a frontal aperture of the shell 702, in which case theelbow would include a conduit that delivers breathable gas from a sourceto the frontal aperture.

The shell 702 includes at least one aperture 708, in this case formed ina rectangular shape to make it easily visible. The aperture 708 isstructured to continuously vent CO₂ during administration of CPAP orNIPPY therapy, for example. A slidable vent plate 710 includes first,second and third aperture portions 712, 714, 716 that may be selectivelyaligned (via sliding along the direction of arrows A) with the aperture708. As shown in FIG. 23 a, the second aperture portion 714 is alignedwith shell aperture 708, while FIG. 23 b shows the plate 710 in ashifted position in which third aperture portion 716 is aligned withshell aperture 708. Therefore, the clinician or patient may change theventing characteristics of the mask.

As shown in FIG. 23 c, a partial schematic cross-section of FIG. 23 a,the vent plate 710 may be releasably held by the shell 702. For example,the shell 702 may include a pair of legs 702 a each forming a groove 702b with which a leg portion 710 a of the plate 710 may slidingly engage.

FIG. 24 shows an alternative form of the invention in a nasal mask 400.This form of the invention includes a hinged vent cover 410. In the formshown in FIG. 24, the vent cover is generally rectangular and one sideis hinged. Similarly to the vent assembly shown in FIGS. 22 and 23, theholes of FIG. 24 may be moulded into a removably insertable grommet 425.The vent cover 410 can alternatively block the set of small vent holes430 and the set of large vent holes 420.

FIGS. 25 a and 25 b show an embodiment of the invention 500incorporating a rotating vent cover 510 in a first and second positionrespectively on a vent elbow. The vent cover 510 is generally discshaped having a window 525 therethrough. By rotating the vent cover 510through, for example 120° different sets of holes are exposed. In theview shown in FIG. 25 a, a set of large holes 520 are exposed. In theview shown in FIG. 25 b a set of small holes 530 are exposed. Eachrespective set of holes 520, 530 provides a conduit communicating withan interior of the mask. In an alternative form (not shown) therotatable vent cover includes different sets of holes and there is afixed position window to which the vent cover is attached. Rotating thevent cover presents a different set of vent holes to the windowresulting in a different vent characteristic.

FIGS. 25 c-25 e illustrate yet another embodiment of the presentinvention. As shown in the assembled view of FIG. 25 c, a frame 800includes a swivel elbow 802 that may rotate with respect to the frame800. A rear end 803 of the swivel elbow is connected or provided to theframe 800, while the a lower end 805 is connected to a source ofpressurized air or other breathable gas. A vent assembly 806 may beprovided to a front portion of the elbow 802.

FIG. 25 d shows the frame 800 and elbow 802 without the vent assembly806. Front portion 807 of elbow 802 is similar to that shown in FIG. 7,in that it includes a vent opening 809 that continuously exhausts CO₂ toatmosphere. In the case of FIG. 7, exhausted air is initially directedto vent cover 70 (see FIG. 2) provided to cover the front portion of theelbow, and then the exhausted air is directed to atmosphere via one ormore apertures 50.

As shown in FIG. 25 d, at least a portion 810 is closed or blocked, sothat air may not pass therethrough. Thus, exhausted air is directedsolely through that portion of the elbow including vent opening 809.Once air is exhausted through opening 809, it is directed to ventassembly 806. In particular, the exhaust can be selectively directed toeither first vent portion 812 or second vent portion 814, as shown inFIG. 25 c.

First vent portion 812 may be similar to the vent cover in FIG. 2, inthat it can be made of an elastomeric material that is stretched to fitover a lip 813 provided to the front portion 807 of elbow 802. The firstvent portion 812 may include one or more apertures 816 to exhaustexhaled gas. The first vent portion 812, unlike the vent cover in FIG.2, may rotate with respect to the elbow 802. Rotation allows the user orclinician to select whether exhausted gas is directed to the first orsecond vent portion 812, 814.

FIG. 25 e shows vent assembly 806 in isolation. Vent assembly 806 anopening 818 adapted to be engaged with the rim 813 positioned on frontportion of elbow 802. Vent assembly includes an interior wall member 820which partially divides the second vent portion 814 from a chamber 822in communication with first vent portion 812. The chamber 822 and thesecond vent portion 814 can be in communication with one another viainterior aperture 824, depending on the relative position of the ventassembly 806 with respect to the elbow 802.

For example, if the vent assembly is rotated so that the interior wallmember 820 is aligned with blocked portion 810 of elbow 802 (FIG. 25 d)and the aperture 824 is aligned with aperture 809, then exhausted gascan be directed through second vent portion 814. In this position, aportion of the exhaust could also be vented through first vent portion812. If the aperture 824 is aligned with blocked portion 810, thenexhausted air would be directed solely to first vent portion 810.Preferably, the blocked portion 810 may include an elastic material thatcan easily form an air tight seal with respect to aperture 824.

The second vent portion 808 may be in the form of a cylinder that couldbe filled with foam 815, to reduce noise and/or the possibility ofcross-infection. As an alternative to foam, a ceramic material orGORE-TEX™ could be used.

FIGS. 25 f and 25 g show yet another vent assembly 830, which, e.g., isadapted for use with the frame and elbow shown in FIG. 25 d. Ventassembly includes a first vent portion 832 (FIG. 25 g) like first ventportion shown in FIG. 25 c. Vent assembly 830 includes a second ventportion 834 which includes a plurality of apertures 836. Exhausted airis selectively directed to the first or second vent portion, dependingon the relative rotational position of the vent assembly compared to theelbow, with interior wall member 838 being selectively aligned witheither the aperture 809 or the blocked portion 810 of elbow 802 (FIG. 25d). In FIG. 25 f, the second vent portion 834 can be seen throughaperture 840. FIG. 25 f also shows opening 842 adapted to be engagedwith rim 813 (FIG. 25 d). The vent assembly 830 is more compact than thevent assembly shown in FIG. 25 e.

FIGS. 26, 27 a and 27 b show an alternative form of the inventionincluding a replaceable vent cartridge. In this form of the inventionthe vent assembly comprises a shaft 600, a rotatable sleeve 620including a window 625 and a replaceable cartridge 630 with holestherethrough. The vent assembly is shown in exploded view in FIG. 26.When assembled, the cartridge 630 is slid into position over the shaft600 and under the sleeve 620. In the form shown in FIG. 27 a-27 b, inuse the cartridge 630 is designed to be not rotatable about alongitudinal axis of the shaft 600. In contrast, the sleeve 620 isdesigned to be so rotatable exposing a different set of holes in thecartridge 630 as shown in FIGS. 27 a and 27 b. In use the holes of thecartridge 630 provide for fluid communication from the interior of theshaft 600 to atmosphere. Because small vent holes can become cloggedwith use, the sleeve 620 can be rotated after a suitable period (e.g.overnight). One cartridge might thus provide each night a clean set ofvent holes for a week without requiring cleaning. At the end of theweek, the cartridge may be disposed of a replaced with a clean one.

Advantages of the Invention Include

When in the quiet position (fine holes) the mask will be extremelyquiet, and with no discernable air jets. This makes the mask far lessdisturbing to both the wearer and any bed partner.

When in the normal (large holes) position, the mask will be suitable foruse with a humidifier which might clog smaller holes. When thehumidifier is not needed, the vent assembly can be switched easily tothe quiet, small hole vent.

The use of a moveable part means that the patient does not need to keepspare parts and is precluded from losing components or not being able tofit them.

Use of the invention enables masks to be compatible with a range ofdifferent flow generators or blowers. For example, a first flowgenerator or blower may be pre-programmed to operate assuming a firstvent characteristic and a second blower, a second vent characteristic.Since the same mask can mimic different vent characteristics, the samemask can be used on both blowers once set to the appropriate vent.

Another advantage of the invention is to provide different vents fordifferent pressure ranges. For example, at low pressures, it may beappropriate to have a vent with large holes in order to providesufficient vent flow. The same vent at higher pressures would haveunnecessarily high vent flow which leads to increased noise. Hence inaccordance with an embodiment of the invention, when a patient is usinga generally low pressure treatment, they can utilize a first vent, butwhen treatment pressures are higher they can use a second vent.

Another advantage of the invention is that it provides a quick andsimple system of replacing disposable vents. For example, certain stylesof vents may clog easily and be designed for a single night's use. Inaccordance with an embodiment of the invention a vent assembly cancomprise a set of “single use” vents. After a first night's use, thepatient can switch to the second vent. After a second night's use, thepatient can switch to a third vent, and so on.

In another form of the invention, sensors and/or indicators are includedin the vent assembly as shown in FIGS. 20 & 21. The vent assembly 300includes a shaft 302 and a sleeve 304. The shaft 302 includes an orifice306 which allows air to pass through. By rotating the sleeve 304alternative vents 308 and 310 are aligned over the orifice 306. Thesensor detects which of the vents is being used and conveys theinformation to a flow generator controller. In one form the sensor has adifferent electrical resistance, depending on the vent being used, asshown in FIG. 21 and discussed further below. Sensor information may beconducted to the flow generator controller via wires along the airdelivery conduit, or wirelessly, for example via a BLUETOOTH™ compatiblesystem. The flow generator controller receives the sensor informationand adjusts the parameters for the algorithms controlling therapy.Alternatively or additionally the vent assembly includes an indicator ofvent position which may be visual, aural, tactile or some combination.As shown in FIG. 20, the vent assembly 300 includes an alignment arrow312 moulded on the shaft 302. Each vent 308, 310 has an adjacentindicator (e.g. an arrow, dot or some other shape) 309, 311 molded ontothe sleeve 304. The indicators may present a characteristic feeldepending on the vent position so that they can be recognized in thedark. Additionally or alternatively, the vent assembly may exhibit acharacteristic “click” as its vent is changed as shown in FIG. 20. Thevent assembly may display a tag of different color depending on the ventposition.

FIG. 21 shows schematic of a slidable cover 350 forming part of the ventassembly similar to FIG. 11-14. When the appropriate vent 352 or 354 isaligned over an orifice (not shown), a corresponding resistor 353 or 355electrically connects to a connector 356 which is in electricalcommunication with a flow generator controller 358. Thus the flowgenerator controller 358 can detect which vent is being used and adjustpressure, flow or some other parameter of the blower as necessary.

This ability to communicate the selected vent to the flow generatorallows for the flow generator to provide an appropriate response. Aresponse may be to make an adjustment to its control algorithm takinginto account the characteristic of the recognized selected vent. Inaddition or alternatively the flow generator may not operate intreatment mode or only operate within a predetermined pressure rangewhen the user attempts to commence treatment having selected the lessthan optimum vent or the characteristics of the selected vent is notrecognized by the flow generator.

In addition or alternatively the flow generator may prompt the selectionof the optimum vent for a given control algorithm or air circuitconfiguration. Having detected the selection of a vent the flowgenerator may present a messages to the user. The message may be by wayof an auditory or visual alarm. Through use of the flow generator statusdisplay (typically an alpha-numeric LCD panel) the flow generator maypresent a statement as to the detected vent condition and either confirmits appropriateness or suggest corrective action.

As the invention allows for a selection to be made between vents theflow generator may communicate to the user that a selected vent issatisfactory or unsatisfactory depending on the treatment pressure rangeit is set to deliver. For a higher pressure range the flow generator mayprompt the use of a small hole vent while suggesting a larger hole ventwhere it is to operate in the lower pressure range.

If the flow generator can detect a deterioration of vent performanceover time (for example due to the vent becoming blocked during onetreatment session or over a number of sessions) then a prompt may begiven for the selection of an alternative vent.

Such a system is of use where available air circuit configurations mayinclude a humidifier. If the flow generator detects that a small hole(e.g. mesh vent) is selected while the air circuit is set up to operatewith a humidifier the flow generator may send a message to the user inorder to prompt the selection of a more suitable vent.

Flow and noise levels may thus be adjusted in accordance with the aboveembodiments. For example, by switching from a vent with large holes to avent with small holes and/or foam, the flow and/or noise level can bereduced about 5-50%, preferably about 15-35%, and most preferably about20-30%. In the embodiment of FIGS. 11 a-14, the flow for large holes maybe in the range of about 45-55 1/min, while the flow for the small holesmay be about 55-65 1/min. In other embodiments, the difference of flowbetween the smaller and larger holes may be more or less pronounced,depending on patient requirements and mask configuration.

Although the invention has been described with reference to particularembodiments, it is to be understood that these embodiments are merelyillustrative of the application of the principles of the invention.Numerous modifications may be made therein and other arrangements may bedevised without departing from the spirit and scope of the invention.

For example, in the embodiment shown in FIGS. 28 a and 28 b, the mask,e.g., mask 30 in FIG. 1, may be provided with two or more elastic ventinserts each having different flow characteristics. In FIG. 28 a, thevent 31 has a plurality of relatively larger holes 33, while the vent 35in FIG. 28 b may have a larger number of relatively smaller holes 37.The clinician/patient may change the vent to best suit the desired noiseand/or flow characteristics.

1. A patient interface for delivery of a flow of breathable gas at acontinuously positive treatment pressure with respect to ambient airpressure to an entrance to a patient's airways, while the patient issleeping, to ameliorate sleep disordered breathing, said patientinterface comprising: a patient contacting portion to seal against anarea surrounding the entrance to the patient's airways for the flow ofbreathable gas; a frame defining a cavity pressurised at the treatmentpressure; and a gas washout vent configured to allow a flow of patientexhaled CO2 to an exterior of the patient interface to minimiserebreathing of exhaled CO2 by the patient, the gas washout ventcomprising an orifice, a first vent, and a second vent, the gas washoutvent having a first position wherein the orifice is in pneumaticcommunication with the first vent, and the gas washout vent having asecond position wherein the orifice is in pneumatic communication withthe second vent, wherein a first visual indicator is associated withsaid first position and a second visual indicator is associated withsaid second position.
 2. The patient interface of claim 1, wherein athird visual indicator is fixed relative to the orifice.
 3. The patientinterface of claim 1, wherein the first vent comprises a first flowcharacteristic, wherein second vent comprises a second flowcharacteristic, and wherein the first flow characteristic and the secondflow characteristic are different.
 4. The patient interface of claim 3,wherein the first flow characteristic comprises a first cross-sectionalvent area, and wherein the second flow characteristic comprises a secondcross-sectional vent area.
 5. The patient interface of claim 4, whereinthe orifice has a cross-sectional area greater than the firstcross-sectional vent area and the second cross-sectional vent area. 6.The patient interface of claim 5, wherein the patient interfacecomprises a tubular member, the gas washout vent provided on saidtubular member.
 7. The patient interface of claim 6, wherein the gaswashout vent is rotatable about a longitudinal axis of said tubularmember between the first position and the second position.
 8. Thepatient interface of claim 6, wherein the gas washout vent is slidablein a direction parallel to a longitudinal axis of said tubular memberbetween the first position and the second position.
 9. The patientinterface of claim 4, wherein the first cross-sectional vent area isgreater than the second cross-sectional vent area, and wherein a firsttreatment pressure associated with the first cross-sectional vent areais smaller than a second treatment pressure associated with the secondcross-sectional vent area.
 10. The patient interface of claim 1, whereinthe gas washout vent is configured to provide visual, tactile, and/oraudible feedback to the patient when the gas washout vent is changedbetween the first position and the second position.
 11. The patientinterface of claim 1, wherein the gas washout vent is positioned on theframe.
 12. The patient interface of claim 1, further comprising a swivelelbow, wherein the gas washout vent is positioned on the swivel elbow.13. A patient interface for delivery of a flow of breathable gas at acontinuously positive treatment pressure with respect to ambient airpressure to an entrance to a patient's airways, while the patient issleeping, to ameliorate sleep disordered breathing, said patientinterface comprising: a patient contacting portion to seal against anarea surrounding the entrance to the patient's airways for the flow ofbreathable gas; a frame defining a cavity pressurised at the treatmentpressure; and a gas washout vent configured to allow a flow of patientexhaled CO2 to an exterior of the patient interface to minimiserebreathing of exhaled CO2 by the patient, the gas washout ventcomprising a first member structured to conduct the flow of gastherethrough and a second member disposed about the first member, atleast one of the first member and the second member having a tubularshape, wherein the first member has a longitudinal axis and the secondmember is slidable axially along the longitudinal axis, and wherein thefirst member comprises an orifice and the second member comprises afirst vent and a second vent.
 14. The patient interface of claim 13,wherein the gas washout vent has a first position wherein the orifice isin pneumatic communication with the first vent, and the gas washout venthas a second position wherein the orifice is in pneumatic communicationwith the second vent.
 15. The patient interface of claim 13, wherein thefirst vent has a first flow characteristic and the second vent has asecond flow characteristic, and wherein the first flow characteristicand the second flow characteristic are different.
 16. The patientinterface of claim 15, wherein the first flow characteristic comprises afirst cross-sectional vent area, and wherein the second flowcharacteristic comprises a second cross-sectional vent area.
 17. Thepatient interface of claim 16, wherein the orifice has a cross-sectionalarea greater than the first cross-sectional vent area and the secondcross-sectional vent area.
 18. The patient interface of claim 16,wherein the first cross-sectional vent area is greater than the secondcross-sectional vent area, and wherein a first treatment pressureassociated with the first cross-sectional vent area is smaller than asecond treatment pressure associated with the second cross-sectionalvent area.
 19. The patient interface of claim 13, wherein the gaswashout vent is configured to provide visual, tactile, and/or audiblefeedback to the patient when the gas washout vent is slid along thelongitudinal axis.
 20. The patient interface of claim 13, wherein thegas washout vent is positioned on the frame.
 21. The patient interfaceof claim 13, further comprising a swivel elbow, wherein the gas washoutvent is positioned on the swivel elbow.
 22. A patient interface fordelivery of a flow of breathable gas at a continuously positivetreatment pressure with respect to ambient air pressure to an entranceto a patient's airways, while the patient is sleeping, to amelioratesleep disordered breathing, said patient interface comprising: a patientcontacting portion to seal against an area surrounding the entrance tothe patient's airways for the flow of breathable gas; a frame defining acavity pressurised at the treatment pressure; and a gas washout ventconfigured to allow a flow of patient exhaled CO2 to an exterior of thepatient interface to minimise rebreathing of exhaled CO2 by the patient,the gas washout vent comprising a first member and a second member,wherein the first member has a longitudinal axis and the second memberis rotatable about the longitudinal axis, wherein the first membercomprises an orifice and the second member comprises a first vent and asecond vent, and wherein a cross-sectional area of the gas washout ventis defined by a portion of the orifice aligned with the first vent orthe second vent.
 23. The patient interface of claim 22, wherein the gaswashout vent has a first position wherein the orifice is in pneumaticcommunication with the first vent, and the gas washout vent has a secondposition wherein the orifice is in pneumatic communication with thesecond vent.
 24. The patient interface of claim 22, wherein the firstvent has a first flow characteristic and the second vent has a secondflow characteristic, and wherein the first flow characteristic and thesecond flow characteristic are different.
 25. The patient interface ofclaim 24, wherein the first flow characteristic comprises a firstcross-sectional vent area, and wherein the second flow characteristiccomprises a second cross-sectional vent area.
 26. The patient interfaceof claim 25, wherein the orifice has a cross-sectional area greater thanthe first cross-sectional vent area and the second cross-sectional ventarea.
 27. The patient interface of claim 25, wherein the firstcross-sectional vent area is greater than the second cross-sectionalvent area, and wherein a first treatment pressure associated with thefirst cross-sectional vent area is smaller than a second treatmentpressure associated with the second cross-sectional vent area.
 28. Thepatient interface of claim 22, wherein the gas washout vent isconfigured to provide visual, tactile, and/or audible feedback to thepatient when the gas washout vent is slid along the longitudinal axis.29. The patient interface of claim 22, wherein the gas washout vent ispositioned on the frame.
 30. The patient interface of claim 22, furthercomprising a swivel elbow, wherein the gas washout vent is positioned onthe swivel elbow.